Leaf spring design 4

• Apr 14, 2004

2
• #2

israelkk

Aerospace

Dec 30, 2002

2,280

MANUAL ON DESIGN AND APPLICATION OF LEAF SPRINGD - SAE HS J788 FOURTH EDITION 1982. There maybe a newer one.

 

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• Apr 14, 2004

2
• #3

GregLocock

Automotive

Apr 10, 2001

23,781

That would be a great place to start. It is also fairly easy to design them from scratch, using a spreadsheet and classic beam theory.

However, to get you going, here is the formula for a multileaf spring, from the Bosch Blue Book

Bending stress= 3*length*Force/(width*N*thickness^2)

N is the number of leaves in the middle, n is the number at the end

rate=(2+n/N)*E*N*width*thickness^3/(6*length^3)

This leaf spring is triangular in side view, ie each leaf is a fixed amount shorter than the one above.

The Devil is definitely in the details, which is where the SAE book will help.

Cheers

Greg Locock

 

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• Apr 18, 2004

• Thread starter
• #4

claver

Aerospace

Mar 6, 2003

45

Hi Greg,

I have had a go at the formula you have shown. Just a few questions ….

If length, width and thickness is in m, Force in Newton’s. N is the number of leaves at the end. i.e. next to the eye … With 8 springs and 2 at the end (1 is the top spring with the eye) The other 6 are then evenly shorter …right ??

The calculated rate is then the movement in m (from the centre of the spring) for each N applied to the spring ??

E = Youngs Modulus for the material used.

Or have I got myself barking up the wrong tree here ….

Appreciate you comments on this …

Jan

 

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• Apr 18, 2004

• #5

GregLocock

Automotive

Apr 10, 2001

23,781

N=8 n=2, everything else you say is correct.





Cheers

Greg Locock

 

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• Apr 19, 2004

• Thread starter
• #6

claver

Aerospace

Mar 6, 2003

45

Hi Creg

Thanks for your reply. I think I must have a decimal error. With ….

L = 0.89m
F = 24516N
W = 0.05m
N = 8
n = 2
t = 0.04m
E = 210000 MN/m^2

The rate is 2.86m … clearly not right ….?? I must have missed something ….

Regards

Jan

 

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• Apr 19, 2004

• #7

NormPeterson

Structural

Sep 11, 2003

1,474

Maybe t = 0.004m?

Norm

 

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• Apr 19, 2004

• #8

NormPeterson

Structural

Sep 11, 2003

1,474

And I think that the formula assumes a symmetrical spring package with the axle located at the midpoint as seen in side view and defines the length "L" as being from the axle to either eye rather than being the overall length of the spring between the eyes.

Norm

 

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• Apr 19, 2004

• #9

GregLocock

Automotive

Apr 10, 2001

23,781

Yes, L is perversely the half length of the spring.

I don't see how you got 2.86, I think you've got an arithmetic error.

I'd use a t of more like .015, and more leaves, for this design.

You probably want 400-2000 N/mm (roughly) as a rate

Cheers

Greg Locock

 

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• Apr 20, 2004

• Thread starter
• #10

claver

Aerospace

Mar 6, 2003

45

It looks like I am using to many “0” in my value for E …. The error with the thickness did not help matters ! Thanks for point out that L is ½ the physical length of the spring

Regards

Jan

 

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• Apr 22, 2004

• Thread starter
• #11

claver

Aerospace

Mar 6, 2003

45

Hi,

Can you please explain why I can only get a sensible answer when I use 210x10^6 for E. I thought E should have been 210x10^11 (in Newtons)

Regards

Jan

 

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• Apr 22, 2004

• #12

desertfox

Mechanical

Dec 29, 2002

5,560

Hi claver

E for steel should be 210*10^9 N/m^2 or 210*10^9 N/m^2.

regards desertfox

 

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